The December, 1931 absorption experiments by Irene and Fredrick Joliot-Curie using Po Be, PoB and PoLi sources to study penetrating radiation

The December, 1931 absorption experiments by Irene and Fredrick Joliot-Curie using Po Be, PoB and PoLi sources to study penetrating radiation S.M. Shafroth, Physics and Astronomy Department, University of North Carolina at Chapel Hill 27599-3255, shafroth@physics.unc.edu. The experimental arrangement including the Hoffman electroscope radiation detector and samples of the raw data are shown.$^{1}$ The emitted neutrons were interpreted as very high energy penetrating gammas. The exponential decay of detected radiation with thicknesses of Pb from 1.5- 5 cm are shown. I. Curie concludes, based on current knowledge of absorption coefficients vs gamma energy, that the gamma energy from PoBe was 15-20 MeV. However cloud chamber experiments had shown that the ``penetrating radiation'' could eject protons from paraffin with energies of 4.5 and 2 MeV in the case of Be and B respectively. If the ejection mechanism were the Compton effect, the gamma energies had to be 50 and 35 MeV respectively. Finally they conclude that the discrepancy in gamma energies could be ``due to the uncertainties.'' \newline 1. Comptes Rendus de l'Academie des Sciences, S\'{e}ance du 28 Decembre 1931